Due to their light weight and high strength, fiber-reinforced resin members (fiber-reinforced plastics (FRPs)) obtained by mixing a reinforcement fiber material into resin are used in various industries, e.g., automobile, construction, aviation, etc.
By way of example, with respect to the automobile industry, the above-mentioned fiber-reinforced resin members are employed as structural members of vehicles, e.g., pillars, rockers, underfloor floors, etc., and as non-structural members that require design, e.g., door outer panels, hoods, etc. Attempts have thus been made to produce fuel-efficient and environment-friendly vehicles by ensuring vehicle strength while reducing its weight.
While there are a wide range of methods for molding such fiber-reinforced resin members, one example thereof would be a method in which a sheet molding compound method (SMC method) is applied.
By applying this SMC method, and in order to dispose, for example, a unidirectional continuous fiber-reinforced member (UD member) in the surface of a fiber-reinforced resin member at a location where strength is required in particular, this continuous fiber-reinforced member is temporarily attached to cavity surfaces of upper and lower molds, and molten resin is injected into the cavity. Alternatively, a lump or sheet of molten resin preformed by being pre-heated is disposed within the cavity and pressed. A fiber-reinforced resin member in which the UD member is buried in its surface is thus produced.
However, there is a problem in that, when molding is thus performed within the cavity by temporarily attaching the UD member to the cavity surfaces, the continuous fiber forming the UD member becomes disordered upon molding, as a result of which its orientation is disrupted, making the desired strength difficult to attain. As an example of a method of measuring/evaluating bending amount (offset amount), in the event that the unidirectional continuous fiber F, . . . in FIG. 8 before bending, bends as in FIG. 8b, the offset amount of the fiber may be measured and evaluated in a direction perpendicular to the original orientation direction of the fiber (bending amount t mm). Further, according to one finding, when the continuous fiber bends and its angle is consequently offset by 3 degrees, the physical property (tensile strength) of the UD member is known to deteriorate by approximately 10%, or by approximately 50% if it is offset by 12 degrees.
Given the above, Patent Literature 1 discloses an invention in which a recessed part is provided at the boundary between a portion where a unidirectional continuous fiber-reinforced member is to be provided on the surface and all other portions (a protruding part is provided on the cavity surface for the purpose of forming this recessed part), thereby seeking to suppress orientation offset in the continuous fiber forming the continuous fiber-reinforced member.
However, the molded article disclosed in Patent Literature 1 has a problem in that the above-mentioned boundary becomes thinner by an amount corresponding to the recessed part of the cavity, and when an external force acts thereupon, stress is concentrated thereat, making it prone to becoming a fracture origin.
Further, it also has a problem in that, over the course of molding, the continuous fiber-reinforced member temporarily provided on the cavity surface of the upper mold is prone to falling when closing the mold, making it difficult to obtain a molded article with the continuous fiber-reinforced member buried in the surface.